Semi-conductor devices



Dec. 18, 1962 J. R. A. BEALE SEMI-CONDUCTOR DEVICES 2 Sheets-Sheet lFiled Jan. 16, 1959 INVENTOR JULIAN R. A. BEALE AGEN BY M Dec. 18, 1962J, BEALE 3,069,297

SEMI-CONDUCTOR DEVICES 7 Filed Jan. 16, 1959 2 Sheets-Sheet 2 INVENTORJULIAN R. A. BEALE BY i 8 M AGENT United States PatentOifice 3,059,297Patented Dec. 18, 1962 SEMI-CONDUCTOR DEVICES Julian Robert AnthonyBeale, Whitehall Wraysbury, near Staines, England, assignor to NorthAmerican Philips Company Inc., New York, N.Y., a corporation of DelawareFiled Jan. 16, 1959, Ser. No. 787,195 Claims priority, application GreatBritain Jan. 16, 1958 20 Claims. (Cl. 148-15) This invention relates tomethods of manufacturing semi-conductive electrode systems or devices,more particularly transistors, the semi-conductive bodies of whichcontain at least two electrodes provided by fusion in close proximity toeach other. It also relates to semiconductive electrode systems, moreparticularly transistors, manufactured by the use of such methods.

In the manufacture of many kinds of semi-conductive electrode systems,more particularly if intended for use at high frequencies, the problemis frequently involved how to provide by the fusion method two or moreelectrodes at a very short physical distance from each other. In fact, adecrease of the physical distance between the electrodes results in adecrease of the detrimental seriesresistance of the current path in thesemi-conductor and this is beneficial to the behaviour of thesemi-conductive electrode system at high frequencies. A decrease of thephysical distance between the electrodes may be achieved either bydecreasing the geometric distance between the electrodes, or bydecreasing the specific resistance in the current path between theelectrodes, or preferably by means of a combination of the two steps.

Said problems may occur in semi-conductive electrode systems in whichthe adjacent electrodes are of the same type, as is the case forexample, in the manufacture of field-effect transistors, in which anohmic supply or source electrode and an ohmic discharge or drainelectrode are juxtaposed on one side of the semi-conductive body, theelectrodes being separated by a groove in the semi-conductive body whichnarrows the current path between said electrodes above a blocking layer.In such a fieldefiect transistor it is important for the parts of thecurrent path located outside the narrow portion to have as low aresistance as possible with respect to the resistance of the currentpath in the narrow portion which is effective for the control.

The problem is even more difficult in semi-conductive electrode systemsin which the adjacent electrodes are of different types, 'for exampleone of the n-type and the other of the p-type, as is the case, forexample, in a diffusion transistor, in which the emitter and the basewhich are of different types must be provided side by side on a diffusedlayer. In this case also, a decrease of the physical distance, forexample by decreasing the geometric distance, and/ or decreasing theseries-resistance of the current path in the semi-conductor, is ofparamount importance since it results in a decreased resistance of thebase and hence an improvement of the frequency behaviour.

For providing by fushion two or more adjacent electrodes, use isfrequently made of a jig which consists, for example, of a thin plate ofinert material which is disposed on the semi-conductive body and inwhich two or more holes of the shape desired for the electrode areprovided with the desired spacing. The electrode bodies to be providedby fusion are brought through the said holes onto the semi-conductivebody, the spacing between them thus being fixed during the fusionprocess. However, it will be evident that the shortest distanceobtainable between the electrodes with such a template is limited to theminimum thickness of the wall between the holes which is permissible inview of the mechanical strength and the separate filling of the holes.In addition, the manufacture of such templates is difiicult and the usethereof expensive, inter alia, because they can be employed only a fewtimes as a result of wear.

An object of the invention is inter alia to provide another particularlysuitable method of providing by fusion two adjacent electrodes, whichmethod is simple and may be arranged in many ways into the process ofmanufacturing such semi-conductive electrode systems, the said methodbeing serviceable up to extremely small geometric distances between theelectrodes. The method according to the invention as such is also verysuitable for the manufacture of semi-conductive electrode systems inwhich the tWo adjacent electrodes are different and more particularlyof'different types. The invention also provides inter alia a methodwhich permits of obtaining in a simple manner. extremely short physicaldistances since it permits of reducing not only the geometric distancebut also considerably decreasing the residual series-resistances betweenthe electrodes.

According to the invention, for manufacturing a semiconductive electrodesystem, for example a transistor, the semi-condutive body of whichcontains two electrodes provided by fushion at close proximity to eachother, an electrode is provided by fusion on the semi-conductive bodyover a continuous and large area of the surface, whereafter at least themetal part of the electrode is di' vided into at least two parts byforming'a narrow groove in the solidified material, which groove extendsat least to the recrystallized semi-conductive zone of the electrode,whereafter the separate parts of the electrode are fused again at leastpartly, without allowing them to fuse together. The groove is preferablyprovided. to extend at least into the recrystallized zone. In certaincases it is very favourable for the groove to penetrate even more deeplythan the zone under the electrode infiuenced by diffusion and/orsegregated during the first treatment. The more deeply the groove isprovided in the body, the higher may be the temperature during thesecond fushion treatment. However, it is to be noted that the depth ofpenetration should, of course, not be chosen greater than necessary inconnection with the second fusion treatment and the electrode structuredesired.

The second fusion treatment may be carried out in many favourable waysto the benefit of the semi-conductive structure. According to oneparticular aspect of the invention, an active impurity is added to atleast one of the separate parts of the electrodes, before or during thesecond fusion step, whereby two adjacent different electrodes areobtained after the second fusion step. This aspect is very importantinter alia in the manufacture of semi-conductive electrode systems inwhich the two adjacent electrodes provided by fusion are required to beof opposite types, as is the case for example, in a p-n-p or an n-p-ntransistor, in which the adjacent base and emitter are of oppositetypes, for example, the one of the p-type and the other of the n-type.In the manufacture of such semi-conductive electrode systems, such anactive impurity is added to at least one of the separate parts of theelectrode before or-during the last mentioned fusion treatment, so thatadjacent electrodes of opposite conductivity type are obtained.

Although it is possible to obtain the difference be tween the electrodesby adding the active impurities to one or more of the said parts onlyduring the second fusion treatment, this addition is preferably carriedout in a separate step after forming the groove and before the secondfusion treatment, the second fusion treatment then being used to causethe electrode or electrodes to absorb the active impurity added bysegregation or diffusion. Thus, for example, it is possible in a simpleand suitable manner to obtain a semi-conductive electrode system moreparticularly a transistor, having two adjacent electrodes of oppositetypes by providing by fusion an electrode material containing donorsduring the first fusion treatment intended for obtaining the electrodeover a continuous surface, whereby an n-type electrode is formed, andafter forming the groove adding a material containing an acceptor to oneof the solidified separate parts, whereafter during the subsequenttreatment a p-type electrode is formed at one side of the groove due tothe over compensating action of the acceptor and an n-type electrode isformed at the other side of the groove. It will be evident that theamount of acceptor added must be such that during the segregationprocess it can dominate the donors present in the electrode-melt to beformed. Consequently, for the active impurity to be added, use ispreferably made of an impurity having a segregation constant higher thanthat of the impurity already available. Acceptors suitable for thispurpose in germanium are, for example, the elements gallium, aluminumand boron, more particularly aluminum.

The same structure with electrodes of opposite type provided side byside by fusion may alternatively be obtained in a different manner.Thus, it is also possible to provide by fusion an electrode materialcontaining acceptors during the first fusion treatment intended forobtaining the electrode over a continuous area of the surface, where bya p-type electrode is formed and after forming the groove to add amaterial containing donors to one of the separate solidified parts,whereafter during the subsequent fusion treatment an n-type electrode isformed at one side due to the overcompensating action of the donor and ap-type electrode is formed at the other side of the groove. In thiscase, the added amount of donors must be such that during thesegregation process it can dominate the acceptors Present in theelectrode melt to be formed. Consequently, in this case, use ispreferably made of a donor impurity having a segregation constant higherthan that of the acceptor already available.

In a further particularly suitable method according to the invention,such an electrode structure may also be obtained by providing by fusionan electrode material which is suitable as a carrier material for activeimpurities such, for example, as lead, bismuth, tin or similar material,during the first fusion treatment intended for obtaining the electrodeover a continuous area of the surface and, after forming the groove, byadding a material containing an acceptor to the solidified material atone side of the groove and a material conatining a donor to the materialat the other side of the groove, Whereafter during the subsequent fusiontreatment a ptype electrode is formed at one side of the groove and ann-type electrode at the other side thereof.

It will also be evident that the invention also affords many furtherpossibilities of acting upon the two halves of the electrode. Thus, itis possible, for example, in addition to reversing the conductivity typeof one electrode, to influence at the same time the conductivity of theother electrode by adding an additional proportion of the impurityalready present to the other electrode prior to the second fusiontreatment.

It is readily possible to manufacture a p-n-p or n-p-n transistor in theabove-described manners. The electrode corresponding in type to theunderlying semi-conductor may be used as the base and the electrodewhich is opposite thereto in type may be used as the emitter. The basezone of the transistor may be provided in different ways. Thus, it ispossible, for example, to utilise a semi-conductive body which haspreliminarily been provided with a zone intended as the base zone, forexample a semi-conductive body of the p-type, which has a diffused zoneof the n-type located at its surface. The two electrodes may be providedon this zone by the use of theinvention. Thus, it is possible first toprovide by fusion a donor material on the n-type diffused zone forobtaining the electrode over the continuous area and, after forming thegroove which has a depth of penetration smaller than the diffused zone,to provide one half of the electrode, which is intended as the emitter,with a proportion of an acceptor, so that a p-type electrode is formedat this side of the groove during the second fusion treatment.

According to a further aspect of the invention, which is applicableinter alia to the manufacture of a semiconductive electrode systemhaving adjacent electrodes of opposite types, an active impurity isdiffused into the semi-conductive body during one or more of the fusiontreatments. Preferably, the underlying base zone is formed in the bodydue to the diffusion, during one or more of the fusion treatments, sothat it is possible to use a semi-conductive body which is homogenouslyof a given type. The active impurity to be diffused into the body may besupplied during the relevant fusion treatment from the ambientatmosphere and/ or from the electrode material itself, to which it mayhave been added during one of the preceding steps. From there thediffusing impurity may diffuse into the body throughout its surface viathe free surface of the body and via the fronts of the melts ofelectrode material formed. If the base zone is formed only during one ofthe fusion treatments, the type of the impurity to be diffused into thebody is opposite to that of the initial semi-conductive body.

According to the invention, the diffusion of the active impurity ispreferably effected, at least to a considerable part or substantially,during a fusion treatment after forming the groove. This affords interalia the advantage that a low-ohmic surface is formed in the side wallsof the groove so that the series-resistance and hence the physicaldistance between the electrodes is reduced further. This low-ohmicsurface is also favorable for a low noise level and the stability of theelectrode system. In addition, this method is simple and controllableand may lead to a high reproducibiiity. If the second fusion treatmentis used for the diffusion and for inverting the conductivity type of oneof the electrodes, the diffusing impurity is preferably chosen so thatits speed of diffusion into the semi-conductor at the relevanttemperature is higher than that of the impurity intended for inverting,if they are of opposite type, while for inverting the conductivity typeit is necessary for the content of diffusing impurity and/or itssegregation constant in the electrode material to be less than that ofthe segregating impurity. According to a further simple and efiicaceousembodiment of the method according to the invention, the impurity to bediffused into the body is already added to the electrode material to beprovided by fusion during the first fusion treatment and diffuses fromthe electrode material into the body after forming the groove during thefusion treatment. Although preferably the base zone is provided in thebody due to the diffusion during the second fusion treatment, thediffusion during the second fusion treatment may also advantageously beused in those cases in which the base zone has already been provided inthe body beforehand, since in such cases also the diffusion permits ofobtaining in the side walls of the groove a reduction of theseries-resistance in the current path between the electrodes.

The method according to the invention may also advantageously be appliedto the manufacture of semi-conductive electrode systems in which theadjacent electrodes provided by fusion are of the same type, as is thecase, for example, in a field-effect transistor, in which the ohmicSource electrode and the ohmic drain electrode are provided side by sideon a zone of a given conductivity type, a groove between said electrodesin the base Zone narrowing the current path above the p-n transition tothe adjoining zone of the rectifying gate electrode. An active impurityis diffused into the body during one or both fusion treatments, butpreferably to a considerable part during the second fusion treatment. Asregards this diffusion, the method according to the invention affordspossibilities and advantages for such semi-conductive electrode systemsquite similar to those mentioned in the foregoing or hereinafter withregard to the manufacture of semi-conductive electrode systems havingelectrodes different in type. Thus, for such semi-conductive electrodesystems, also the diffusion may be utilized in similar manners forrendering the surface of the groove low-ohmic and/or for providing thebase zone of the field-effect transistor, the diffusing impurity beingsupplied either from the surrounding atmosphere and/or from theelectrode material itself. For a field-effect transistor also thelow-ohmic surface in the groove is favourable for the noise level andthe stability. Only inverting one electrode can be omitted in this case.

When using a method according to the invention in which a base zone isprovided by diffusion during the second fusion treatment the depth ofpenetration of the melt front of the electrode material into thesemi-conductive body during the fusion treatment after forming thegroove, is preferably chosen greater than that of. the melt front duringthe first fusion treatment. This may be achieved, for example, bychoosing the temperature of the second fusion treatment to besufficiently higher than that of the first fusion treatment. Thisaffords during diffusion inter alia the advantage that the base zone isdiffused from the melt front newly formed, so that the thickness of thebase zone is substantially independent of the depth of penetration ofthe melt front and hence extremely reproducible. In addition, moregenerally the advantage is obtained that the active portion of thesystem is displaced to penetrate the semi-conductive body more deeply sothat there is less risk of the electric properties being detrimentallyinfluenced by any residual disturbances in the crystal lattice near thegroove. However, it will be evident that the depth of penetration of thegroove must be greater than that of the melt front during the secondfusion treatment in order to prevent the two parts from fusing together.

The groove may be formed in any suitable manner. Thus, for example, ithas been found particularly favourable to use for this purpose anultrasonic cutting method which utilises a thin ultrasonic head incombination with a fine abrasive or abrasive slurry. Another methodisone wherein a thin wire coated with a fine abrasive or in combinationwith an abrasive, for instance an abrasive slurry, is reciprocated atthe area concerned. Said methods may be combined, for example, with anafter etching treatment for the groove. Widths of 25 microns in thenarrowest part of the groove may thus readily be obtained. It is thusalso possible for the depth of penetration of the groove to be chosengreater than that of the melt front or of the recrystallized zone of theelectrode, in order topermit the depth of penetration of the melt frontduring the second temperature treatment to be chosen greater than thatduring the first fusion treatment.

A third electrode, for example the collector electrode in the p-n-p orn-p-n transistor, or the gate electrode in the field-effect transistor,may be provided in a simple manner by alloying on the opposite side ofthe semi-conductive body.

A material containing a donor or an acceptor may be either a donorimpurity or an acceptor impurity itself or alloys or mixtures thereofwith other suitable elements. Thus, for example, in those cases inwhich, during the fusion treatment, a donor material is to be alloyed aswell as diffused, it is possible to use one and the same suitable donorimpurity for both purposes, or to use, for example, an electrodematerial containing two donors, one of which has a dominant functionduring alloying because of its higher segregation constant, and theother of which has a dominant function during diffusion because of itsgreater diffusion velocity. In addition, use

may be made with great advantage of an electrode material whichsubstantially consists of a material which itself need not be suitableas an active impurity, but is particularly suitable, for example, onaccount of the low solubility of the semi-conductor in this material orbecause of its suitable mechanical properties as a carrier material forthe active impurities. Examples of such carrier materials in connectionwith germanium are, for example, lead, indium and bismuth, and inconnection with silicon, for example lead.

In order that the invention may be readily carried into effect, severalaspects of the invention will now be explained in detail by way ofexample, with reference to the accompanying diagrammatic drawings inwhich:

FIGS. 1 to 5 show in section the sequential stages of a transistorduring its manufacture by a method according to the invention;

FIG. 6 is a plan view of another embodiment of a transister in a givenstage of the manufacture according to the invention.

In FIGS. 1 to 5, the cross-hatching is omitted for the sake of clarity.

A thin disc of electrode material is provided by melting on, and thusadherent to, a rectangular mono-crystalline semi-conductive slice 1 ofp-type germanium having a specific resistance of 2 ohms/ cm. Thedimensions of the semi-conductive slice are about 1 mm. by 2 mms. by 150microns. The disc of electrode material has a diameter of about 200microns and a thickness of about 50 microns and it consists of lead, towhich 1% by weight of antimony has been added. The electrode materialmay be provided, for example, by heating the semi-conductive slice andthe disc of electrode material placed on it approximately centrally ofone of the large sides in an atmosphere of hydrogen to about 700 C. forabout 3 minutes.

FIG. 1 shows the stage obtained after heating. On the unchanged p-typepart 1 of the semi-conductive body an n-type zone 2 has recrystallizedduring cooling due to segregation of the antimony. This n-type zone 2 ishas been added. The layer 3 constitutes the metal part of the electrode.Line 4 marks how deeply the molten electrode material has penetrated theotherwise solid body. Dimension a in the figure, is about microns anddimension b is about 200 microns. During heating, the antimony candiffuse along the surface of the plate 1 and thus penetrate thesemi-conductive plate via its surface. In addition, the antimony canpenetrate the zone 1 via the junction surface 4 between the melt ofelectrode material and the semi-conductive plate. This is dependent uponthe temperature and the duration of the fusion treatment. However, thedepth of penetration of the diffusion is small at the given temperatureand duration and hence the diffused layer under the surface is not shownfor the sake of clarity, but indicated only under the melt front 4 inthe zone 5.

A thin groove 6 radially provided through the layer 3 penetrates thezone 1 of the plate via layer 3 and zone 2 Said groove is formed bymeans of an ultrasonic cutting method in which use is made of a thincutting blade and a paste of a very fine aluminum-oxide abrasive. Thegroove has a width of only about 25 microns at its bottom and isslightly V-shaped due to abrasion of the sides of the groove as thecutting treatment proceeds further.

The whole is subsequently subjected to an etching treatment at 70 C. forabout 5 minutes in a bath of 20 vol. percent of hydrogen peroxide. Theetching agent removes about 2.5 microns from the surface of thegermanium and hence semi-conductive material damaged during. theultrasonic cutting treatment is also removed from the groove. Underthese conditions, said etching treatment also substantially removes thesuperficial n-type diffused layer formed by the diffusion of antimonyalong the surface, from the surface of zone 1 of the semi-conductivebody.

FIG. 2 shows the semi-conductive body with the electrode cut through atthe stage of the etching treatment. The narrow groove 6 divides themetal layer 3, the zone 2 and the transition 4 into two halves. InFIGURE 2, the parts of the left-hand half of the electrode are indicatedby 3a, 2a and 4a, and the parts of the right-hand half are indicated by3b, 2b and 4b. The new surface of the plate is marked by line 7.

An active impurity of opposite type is added to the right-hand half ofthe electrode. The two halves were of the n-type. Aluminum isparticularly suitable as an acceptor impurity on account of its highsegregation constant. The aluminum may be added, for example, to theright-hand half by providing it by vaporisation onto the surface of thelayer 3b, the surface of the semi-conductive body and that of theelectrode 3a being shielded during evaporation by means of a mask.

The active impurity may alternatively be added in a simple manner, forexample, by providing it in the form of a dispersion in a binder, forexample by means of a brush, on the relevant electrode. A bindersuitable for aluminum is, for example, a solution of methacrylate inxylene.

The whole is subsequently heated in an atmosphere of hydrogen at 950 C.for about minutes, whereby the two halves of the electrode are againfused. After the second fusion treatment, the stage shown in FIG. 3 isreached.

The second fusion treatment is carried out at a temperature sufficientlyhigh to cause the melt front to penetrate the germanium plate moredeeply than was the case during the first fusion treatment. Theadditional parts of the electrode halves provided during the secondfusion treatment are indicated by 9a and 912. Line 10a marks the depthof penetration of the melt front during the second fusion treatment,while the depth of penetration of the first fusion treatment marked byline 4a in FIG. 2 is represented by a dotted line 4a in FIG. 3. Afterrecrystallisation, both the zone 2a and the prolongation thereof, thezone 9a, are of n-type. However, in the right-hand half of theelectrode, the zone 9b and the zone 21), after recrystallisation, havebeen converted into p-type zones 9b and 2b due to the aluminum, duringrecrystallisation, having overcompensated the initial action of theantimony due to the high solubility and segregation constant ofaluminum. In this connection it is to be noted that for overcompensationit is not necessary for the last impurity added to have a segregationconstant higher than that of the first impurity. Over compensating mayalso be obtained with approximately the same value of the segregationconstant or even with a higher segregation constant of the firstimpurity by choosing the content of the second impurity in the melt ofelectrode material to be correspondingly higher than that of the firstimpurity. However, it is usually preferable for the segregation constantand the solubility of the second impurity to be higher than that of thefirst impurity.

The coagulated layer 3b constitutes the metal part of the p-typeelectrode (317', 2b, 9b) and consists of lead, aluminum and antimony andpossibly a small content of germanium. Line 4b of FIG. 2 is representedas a dotted line 41; in FIG. 3.

In addition to recrystallisation and alloying, diffusion also occursduring the second fusion treatment. The antimony upon being provided byfusion, diffuses both from the right-hand part and the left-hand part ofthe electrode via the melt front into the body, while the aluminum onlydiffuses from the right-hand part of the electrode. As a result of thisdiffusion, the p-n transition (not shown) in the right-hand parts lies alittle below the line 10b, which marks the depth of penetration of themelt front in the right-hand electrode. In addition, during the secondfusion treatment, due to the diffusion of the antimony which diffusesmuch more rapidly than does aluminum, an n-type zone 12 is formed whichis internally bounded by line 11, and which extends substantially viathe surface of the groove and below the p-n transition of the right-handelectrode. Due to the diffusion during the second temperature treatment,which took place at a higher temperature and for a longer period thanthe first temperature treatment, a properly defined diffused layer 12and transition 11 are formed as compared to the weak diffusion duringthe first temperature treatment. During this second temperaturetreatment, the parts 3:: and 3b of the electrodes, as shown in FIG. 2,undergo a variation, that is to say, assume the shape of the parts 3aand 3b of FIG. 3. It also appears from FIG. 3 that the electrodematerial upon being provided does not flow into the groove although thegroove is very narrow. In this connection it is noted that thedimensions of the coagulated material after the second fusion treatment,of which the boundary line with the solid material, or in other 'words,the maximum depth of penetration of the melt front is indicated by thelines 10a and 10b, are shown in vertical direction with exaggeration forthe sake of clarity. It is not necessary during the second fusiontreatment to alloy into the semi-conductive plate more deeply thanduring the first fusion treatment. Nevertheless this is preferably done,since in this case the additional advantage is obtained that the basethickness of the transistor is substantially independent of the depth ofpenetration of the electrode material, the thickness of the base zonebeing determined substantially by the diffusion during the second fusiontreatment, which diffusion then takes place from the newly formed meltfronts 10a and 10b. In determining the temperature difference betweenthe first and second fusion treatments, as is necessary for obtainingthe greater depth of penetration of the melt front during the secondfusion treatment, it is neces sary to make allowance for the fact thatloss of electrode material occurs in forming the groove 6. In theexample under consideration, comparatively more lead than antimony isremoved in forming the groove as a result of the difference between thecontents of the two elements in the electrode material.

It will also readily be evident that the groove 6 must be deep enough toavoid that, during the second fusion treatment, the molten material doesnot close off the groove. The depth of the groove must therefore bechosen suitably in connection with the temperature to be used during thesecond fusion treatment.

The electrode system shown in FIG. 3 may be worked into a p-n-ptransistor in the following manner. The surface of the body of FIG. 3located above the dotted line 13, is covered with an etch-resistantlacquer layer consisting of a solution of polystyrene in ethyl methylketone, the whole subsequently being immersed into a 20%hydrogen-peroxide solution heated to 70 C. The treatment is continueduntil the portion of the body heneath the dotted line 13 has beenremoved by etching. The lacquer layer is then removed by immersing thewhole into a bath of ethyl methyl ketone.

Next, a collector is provided on the body by alloying a thin disc ofindium, to which 1% by weight of gallium has been added, on the etchedside of the body opposite the electrodes 3a and 3b. The alloying of thecollector may be effected, for example, by heating the whole in anatmosphere of hydrogen to about 500 C. for 5 minutes. Substantially nofurther diffusion takes place at this comparatively low temperature. Theposition of the collector disc is not critical, but the collector ispreferably provided approximately opposite the layers 3a. and 3b. InFIGURE 4, the reference numeral 14 indicates the recrystalizedsemi-conductive zone of the collector and zone 15 constitutes the metalpart of the collector, which constitutes of an alloy of indium-galliumand a small content of germanium. Soldered on the layer 15, by means ofan indium solder 17, is a rigid nickel member 16 which serves as asupply Wire and also as a support. Thin nickel members 18 and 19 arealso soldered on the metal layers 3a and 3b of the base and the emitterby means of an indium solder 20, 21, respectively. The

soldering process is carried out by means of a small soldering iron.

A transistor system is thus obtained, the supply wires 16, 18 and 19 ofwhich constitute conductors to the collector, the base and the emitter,respectively.

The groove 6 is subsequently filled with a lacquer layer 22 up to alevel located above the zones 2a and 2b by means of a drop of a solutionof polystyrene in ethyl methyl ketone. The lacquer is diluted so that itcan flow freely along the surface of the groove 6 and projects onlyslightly above its ends. After filling with the lacquer up to the levelindicated by a dotted line in FIG. 4 the lacquer is allowed to dry. Thethree supply wires 16, 18 and 19 are then connected to the positiveterminal of a source of supply, the whole subsequently being placed inan etching bath containing a 5% aqueous NaOH-solution. A platinumelectrode is suspended in the etching bath and connected to thenegative'terminal of the source of supply. A current of ma. is adjustedand maintained for about 10 minutes, so that more than 25 microns of thesurface is removed, as shown in FIGURE 5. This figure also shows thatthe etching agent has also etched partly below i the metal parts 3a and3b of the electrodes. In addition,

during etching, the superficial part of the n-type diffused layer hasbeen removed.

The lacquer layer is subsequently removed from the groove 6 bydissolution in ethyl methyl ketone, the whole being immersed in anetching bath of 20% of hydrogenv peroxide for about seconds at 70 C. Thetransistor is subsequently mounted in known manner in an envelope- Thetransistor thus obtained has a low resistance of the base since thegeometrical distance between the base contact 3a and the emitter issmall and, in addition, a current path of a low specific resistanceexists over this extremely, small distance along the surface of thebottom of the groove. The low specific resistance of the surface isbrought about by the diffusion of antimony during the second fusiontreatment, since upon diffusion into a surface there is always aconcentration in the surfaces con siderably higher than at some distancebelow the surface. In the case under consideration, the antimony for thediffusion is supplied from the molten electrode material and theantimony diffuses from there to a high degree along the surface. Thetransistor also has a very low noise level and .a high stability. Theabove-described p-n-p transistor also has a low emitter-base capacityand a low base-collector capacity due to the limitation of the surfaceof the p-n junctions during etching, whereby even a portion below themetal parts of the emitter and the collector has been removed. Due tothe aforementioned exceptional properties, the transistor is verysuitable for use at high frequencies.

FIGURE 6 shows another embodiment of a transistor which may likewise bemanufactured in a similar manner by the method according to theinvention. FIG. 6 is a plan view of this transistor at a manufacturingstage corresponding to FIG. 3. Instead of a straight groove through theelectrode, in this embodiment an annual groove 6 is provided, which isfilled with polystyrene lacquer before proceeding to the second etchingtreatment. The central part 3b constitutes the metal part of theemitter, whereas the outer part 3a constitutes the metal part of thebase. During the second etching treatment, due to the emitter beingfully surrounded by the groove filled with the polystyrene, there willbe no etching below the metal part of the emitter. The emitter-basecapacity is thus higher and this embodiment is not particularly suitablefor use at very high frequencies, although admirably suited for use as amedium power transistor at high 10 frequencies. Manufacturing steps notspecially mentioned in this example are wholly identical with thosedescribed with regard to the transistor shown in FIG. 1 to 5.

It is to be noted that many variations are possible Within the scope ofthe invention. Thus, for example, it is also possible, after the firstfusion treatment, to divide the largearea electrode into more than tWoparts and thus obtain more than two adjacent electrodes provided byfusion. In this case the second fusion treatment may be used for actingupon the conductivity and/ or the conductivity type of one or more ofthe electrodes. Thus, it is also possible in those cases in which afterforming the groove, the type of one electrode must be inverted and thediflfusion of the base zone must be carried out, to perform these twotreatments in two separate fusion treatments. It will also readily beevident that the use of the invention is not limited to the specifiedsemi-conductors germanium and silicon, but that it also comprises othersemi-conductors, for example, the semi-conductive compounds, such as theIII-V compounds, for example GaAs and InP. Further more, the inventionis of course, applicable not only to the manufacture of transistors, butalso to any other semiconductive electrode or devices having at leasttwo adjacent electrodes.

What is claimed is:

l. A method for producing a semi-conductor device comprising providingon a surface of a semi-conductive body a largearea contact, dividing thecontact but not the entire body into plural separated portions,thereafter adding to one of the plural portions an active impuritycapable of altering the conductivity of that contact portion whenincorporated therein, and thereafter fusing the separated contactportions to incorporate the active impurity into that portion to whichit was added thereby to selectively alter its conductivity.

2. A method as set forth in claim 1 wherein the largearea contact isdivided into two halves.

3. A method of providing adjacent regions of different a conductivity ina semi-conductive body, comprising fusing and alloying animpurity-bearing mass to a surface of the semi conductive body toproduce underneath the mass a region of given conductivity type in thebody, thereafter forming a groove into and through the mass and into thesaid region of given conductivity type to divide the mass into at leasttwo separate parts, thereafter adding to less than all of the partsanother impurity capable of altering the conductivity type of theunderlying body region when incorporated therein, and thereafterrefusing the separated masses to incorporate the added impurity into theselected parts and thereby alter the conductivity type of the underlyingregion and make it different from the adjacent region of the said givenconductivity type.

4. A method as set forth in claim 3 wherein the groove extends throughthe said region of given conductivity type thus dividing it into atleast two separate parts.

5. A method as set forth in claim 3 wherein the groove is formedby,cutting by ultrasonic means.

6. A method as set forth in claim 3 wherein the groove is cut byreciprocating a thin wire associated with a fine abrasive in contactwith the mass.

7. A method as set forth in'claim 4 wherein the temperature at which thefirst fusion is carried out is lower than the temperature at which therefusion is carried out.

8. A method of providing adjacent regions of different conductivity in asemi-conductive body, comprising fusing and alloying adonor-impurity-bearing mass to a surface of the semi-conductive body toproduce underneath the mass a region of n-type conductivity in the body,thereafter cutting a slot into and through the mass and into the n-typeregion to divide the mass into two separate parts, thereafter adding toone of the parts an acceptor impurity having a segregation coefficientin the semi-conductive body greater than that of the donor impurity, andthereafter refusing the masses to incorporate the acceptor impurity intothe selected'part and thereby 1 1 alter the conductivity type of theunderlying region and make it p-type.

9. A method as set forth in claim 8 wherein one underlying regionconstitutes the base region and the other underlying region constitutesthe emitter region of a transistor.

10. A method as set forth in claim 8 wherein the slot has an annularshape.

11. A method of providing adjacent regions of different conductivity ina semi-conductive body, comprising fusing and alloying anacceptor-impurity-bearing mass to a surface of the semi-conductive bodyto produce underneath the mass a region of p-type conductivity in thebody, thereafter cutting a slot into and through the mass and into thebody to divide the mass into at least two separate parts, thereafteradding to one of the parts a donor impurity whose segregationcoelficient in the semiconductive body is greater than that of theacceptor impurity, and thereafter refusing the masses to incorporate thedonor impurity into the selected part and thereby alter the conductivitytype of the underlying region and make it n-type.

12. A method of providing adjacent regions of different conductivity ina semi-conductive body, comprising fusing and alloying a metal mass to asurface of the semiconductive body to produce underneath the mass analloyed region, thereafter cutting a slot into and through the mass andinto the body to divide the mass into at least two separate parts,thereafter adding to one of the parts an acceptor impurity and adding tothe other part a donor impurity, and thereafter refusing the masses toincorporate the donor and acceptor impurities into their associatedparts and thereby make the conductivity types of the underlying andadjacent regions of opposite conductivity.

13. A method of providing adjacent regions of different conductivity ina semi-conductive body, comprising fusing and alloying animpurity-bearing mass to a surface of the semi-conductive body toproduce underneath the mass a region of given conductivity type in thebody, thereafter forming a groove into and through the mass and into thesaid region of given conductivity type to divide the mass into at leasttwo separate parts, adding another impurity to one of the separatedparts, refusing the separate parts to incorporate the added impurityinto the underlying body region and thereby alter its conductivity, and,during one of the fusion steps, diffusing an impurity into the body.

14. A method as set forth in claim 13 wherein the diffused impurityforms the same conductivity type as that formed by the impurityoriginally present in the mass.

15. A method as set forth in claim 13 wherein the diffusion step takesplace during the second fusion step.

16. A method of making a semi-conductor device, comprising providing analloyed electrode on a surface of a semi-conductive body. separatingsaid alloyed electrode into two closely-adjacent alloyed electrodes onthe same surface of said semi-conductive body, adding to one only of thesaid separated electrodes a dispersion of aluminum in a binder, andthereafter fusing the separated electrodes to incorporate the aluminuminto the said one electrode and thereby alter its conductivity.

17. A method for producing a semiconductor device comprising forming ona surface of a semiconductive body a large-area fused contact,thereafter forming a narrow groove in the contact which extendscompletely therethrough and into the underlying semiconductive body butnot completely through the latter thereby to divide the contact intoplural separated portions in contact with the same semiconductive body,and thereafter refusing the separated contact portions, but maintainingthem separate, in the presence of an active impurity to incorporate thelatter in a portion of the body thereby modifying its conductivity.

18. A method for producing a semiconductor device comprising fusing andalloying a metal mass to a surface of a semiconductive body to form alarge-area fused contact, thereafter forming a narrow groove in thecontact which extends completely therethrough and into the underlyingsemiconductive body but not completely through the latter thereby todivide the contact into plural separated portions in contact with thesame semiconductive body, and thereafter refusing the separated contactportions in the presence of an active impurity to diffuse the latterinto a portion of the body adjacent the contacts thereby altering itsconductivity.

19. A method as set forth in claim 18, wherein the active impurity ispresent in the atmosphere during the refusion step.

20. A method as set forth in claim 18 wherein a contact portion containsanother active impurity of the opposite-conductivity-forming type whichbecomes incorporated in the adjacent body portion during the refusionstep forming a recrystallized region defining a junction with the bodyportion containing the diffused impurity.

References Cited in the file of this patent UNITED STATES PATENTS2,794,846 Fuller June 4, 1957 2,837,704 Emeis June 3, 1958 2,846,340Jenny Aug. 5, 1958 2,865,082 Gates Dec. 23, 1958 I UNITED STATES PATENTOFFICE CERTIFICATE OF CORRECTION Patent No. 3,069,297 December l8 1962Julian Robert Anthony Beale It is hereby certified that error appears inthe above numbered patent requiring correction and that the said LettersPatent should read as corrected below.

Column 2 lines 24 and. 140,- for fushion-"=- read fusion I column 3 line5O,v for "conatining" read containing column 9-, line 64, for "annual"read annular column 10, line 23, after "elgectrod" insert systems -o.

Signed and sealed this 27th day of August I963 (SEAL) Attest:

ERNEST w. SWIDER DAVID A Attesting Officer Commissioner of Patents 1

1. A METHOD FOR PRODUCING A SEMI-CONDUCTOR DEVICE COMPRISING PROVIDINGON A SURFACE OF A SEMI-CONDUCTIVE BODY A LARGE-AREA CONTACT, DIVIDINGTHE CONTACT BUT NOT